ABSTRACT Based on the framework of social exchange, we hypothesize that early investments made in children will later be reciprocated in the form of instrumental care as parental needs increase. We will examine time-to-death as either an alternative or complementary approach to the use of proxy and self-reports about functional and cognitive impairment to assess vulnerability in older adults in relation to the care-careers of their adult children. The models tested will inform theory about how children serve as conditional resources?responding to their parents? early investments when triggered by parental need?rendering an improved depiction of intergenerational relationships over the family life cycle. The goals of the research are to: (1) link early transfers of valued resources of time, money, and emotion to rates of change in the amount of care adult children provide to their vulnerable older parents; (2) test a novel methodological approach?the ?countdown model??that uses time-to-death to represent a global form of vulnerability that triggers the delivery of care to older parents; and (3) identify whether care to older parents is more strongly associated with time-to-death from Alzheimer's disease and other dementia-related causes compared to other causes. The countdown model uses time-to-death as an alternative, objectively derived metric of biological vulnerability to represent the need for care by aging parents. Our application of this model provides a unique marriage of theory and method that enhances understanding of long-term intergenerational exchange dynamics that unfold over many decades in families, and represents progressive vulnerability of parents using knowledge about the timing and (dementia and non-dementia) causes of their death. Data for this project are derived from the Longitudinal Study of Generations (LSOG), a multi-panel and multi- generational study that has collected data on three-generation families from 1971 to 2016. Focusing on the middle-generation, which averaged 19 years of age in 1971, we examine trajectories of care provided by these children to older mothers and fathers between 1985 and 2016 as a function of accelerating parental vulnerabilities, and their interaction with early investments of time (shared activities), money (financial support), and emotion (intimacy) made in them by their parents in 1971. Using previously collected mortality information about parents from the National Death Index in 2016?combined with an updated NDI search to 2019?we test the utility of time-to-death as a representation of growing cognitive and physical frailty that stimulates children to provide increasing amounts of care. This research is timely in light of growing uncertainty about the family as a reliable source of extended care in later life.